A fuel cell system is used for a Fuel Cell Electric Vehicle (FCEV), which is a type of environmentally-friendly vehicle. The fuel cell system typically includes: a fuel cell stack which generates electric energy from an electrochemical reaction of reaction gases; a hydrogen feeding device which supplies hydrogen gas used as fuel to the fuel cell stack; an air feeding device which supplies air including oxygen used as an oxidizing agent in the electrochemical reaction; and a heat-and-water management system which maintains the optimum operation temperature of the fuel cell stack by dissipating heat from the electrochemical reaction in the fuel cell stack and performs water management.
The fuel cell system is supplied with hydrogen gas and air from an external source and an electrochemical reaction of hydrogen and oxygen occurs in the fuel cell stack of the fuel cell system. During the electrochemical reaction, water is produced from the electrochemical reaction, and the volume of water fluctuates as the water changes into water vapor, saturated liquid, or ice, depending on real-time operating conditions such as temperature and pressure. In other words, water passage may be changed. In addition, the fluctuating volume of water may also influence the channel in a separator, a gas diffusion layer, a catalyst layer, and gases and electrons as water travels through an electrolyte membrane. The fluctuations in the volume of water may result in a flooding state where water overflows in the fuel cell stack or a dehydrated state where water to hydrate the fuel cell stack is insufficient. Particularly, to prevent dehydration, it is necessary to prevent the fuel cell stack from being exposed to high temperature operating conditions, and thus, sufficient cooling may be required.
When the maximum heat dissipation rate of the fuel cell system is reduced due to environmental factors such as a substantially high exterior temperature, an uphill driving condition of a vehicle or other factors such as the failure of cooling components such as a cooling water pump, a cooling fan, a thermostat, and the like; the output current of the fuel cell stack is reduced to maintain the operating temperature of the fuel cell stack at maximum limitation.
In the related art, a conventional technology provides a method of adjusting the temperature of a fuel cell system. For example, the method controls a water pump and a radiator fan to reduce a temperature difference in an inlet and an outlet of a fuel cell stack to a specific temperature range using a temperature distribution detection unit and a load state detection unit.
In another example, a conventional technology provides a control method that includes: segmenting a temperature range of temperatures of cooling water in an outlet of a fuel cell stack into a plurality of classes; setting a target rotating speed for each class; performing a Proportional-Integral (PI) control with respect to rotating speeds of a cooling water pump and a cooling fan based on a detected temperature of cooling water in the outlet of the fuel cell stack such that the temperature of the cooling water in the outlet reaches the target temperature; performing a feed forward control based on a heat value of the fuel cell stack; and adjusting the rotating speeds of the cooling water pump and the cooling fan using a maximum value among values used in the PI control and the feed control.
The foregoing is intended merely to aid in the understanding of the background of the present invention, and is not intended to mean that the present invention falls within the purview of the related art that is already known to those skilled in the art.